In order to satisfy increasing demands on wireless data traffic, wireless communication systems are under development that support higher data transfer rates. Techniques of 4th Generation (4G) systems, which are now being commercialized, are being developed to improve spectral efficiency in general to increase the data transfer rate. However, the techniques of improving the spectral efficiency are not enough to satisfy the explosively increasing demands on the wireless data traffic.
In one method of solving the aforementioned problem, a significantly wide frequency band is used. A frequency band used in a conventional mobile communication cellular system at present is less than or equal to 10 GigaHertz (GHz) in general, and thus it is very difficult to ensure a wide frequency band. Therefore, there is a need to ensure a wideband frequency in a higher frequency band. However, the higher the frequency for wireless communication, the greater the propagation path loss. Accordingly, a propagation distance is relatively short, which results in a coverage decrease. As a method of solving this problem, beamforming techniques are used to decrease the propagation path loss and to increase the propagation distance.
Beamforming can be classified into Transmission (TX) beamforming performed in a transmitting end and reception (RX) beamforming performed in a receiving end. In general, the TX beamforming increases directivity by allowing an area in which propagation reaches to be densely located in a specific direction by using a plurality of antennas. In this situation, aggregation of the plurality of antennas can be referred to as an antenna array, and each antenna included in the array can be referred to as an array element. The antenna array can be configured in various forms such as a linear array, a planar array, etc. The use of the TX beamforming results in the increase in the directivity of a signal, thereby increasing a propagation distance. Further, since the signal is almost not transmitted in a direction other than a directivity direction, a signal interference acting on another receiving end is significantly decreased. The receiving end can perform beamforming on a RX signal by using a RX antenna array. The RX beamforming decreases the RX signal strength transmitted in a specific direction by allowing propagation to be concentrated in a specific direction, and excludes a signal transmitted in a direction other than the specific direction from the RX signal, thereby providing an effect of blocking an interference signal.
As described above, in order to promote wide frequency bands, a super-high frequency band, in other words, millimeter (mm) wave system, may be introduced. In this situation, a beamforming technique is taken into consideration to overcome the propagation path loss. In this technique, a signal subjected to beamforming is transmitted and received starting from an initial access time point. Accordingly, there is a need for a method in which a user terminal obtains synchronization and system information in an environment where beamforming is performed.